1. Field of the Invention
The present invention relates to a noise reduction mechanism of a fan device and a molding method of porous damping material used therefor. More specifically, it relates to a noise reduction mechanism of a fan device used for engine cooling system of special-purpose vehicle including construction equipment such as excavator and other vehicles, and industrial cooling system.
2. Description of Related Art
Conventionally, in an engine cooling system of vehicles, coolant is circulated between the engine and radiator. In such cooling system, a fan is attached proximal to the radiator, so that heat is exchanged between cooling air sucked in by the fan and the coolant in the radiator to cool the engine by the coolant after heat exchange.
In the above, a fan shroud is provided around the fan to straighten flow of the cooling air passing through the radiator, thus enhancing heat exchange by the radiator to improve cooling efficiency of the engine.
A strong swirl is generated at a slight gap between an end of the fan and the fan shroud in accordance with rotation of the fan, which causes jet noise. For reducing the jet noise, it is disclosed in Japanese Utility Model Laid-Open Publication No. Sho 56-41119, Japanese Utility Model Laid-Open Publication No. Sho 57-126524, Japanese Utility Model Laid-Open Publication No. Sho 64-13229 and Japanese Utility Model Laid-Open Publication No. Hei 2-39956 (including microfilm of respective application in the publication) to provide a noise damper to the fan shroud.
All of the noise dampers disclosed in the publications have opposing surface of the fan shroud opposing the end of the fan formed of hard perforated metal with a lot of through-holes being drilled, so that the jet noise can be reduced by the damping material and energy damping space provided further outer side of the perforated metal.
However, according to the noise damper disclosed in the publications, since the perforated metal is used at the portion where the strong swirl is generated, high-frequency impulsive sound can be generated by an impact caused when the cooling air bumps into step portion of the through-holes of the perforated metal. Accordingly, though the noise damper can reduce the jet noise, the impulsive sound can be newly generated, thus being unable to effectively reduce the overall noise.
An object of the present invention is to provide a noise reduction mechanism of a fan device capable of effectively damp both the impulsive sound and the jet noise caused by the swirl, thus effectively reduce the noise.
The noise reduction mechanism of fan device according to the present invention attains the above object by changing material of the member proximal and opposing to the end of the fan and/or structure around the fan (fan shroud).
Specifically, A noise reduction mechanism of fan device according to the present invention includes: a fan shroud spaced apart from a rotation locus of an end of a rotary fan by a predetermined gap; a shroud support for supporting the fan shroud; and a porous damping material opposing to the end of the fan, the porous damping material being attached to at least a part of the fan shroud or forming a part of the fan shroud.
In the present description, the word xe2x80x9cporousxe2x80x9d refers to a material having porosity, i.e. sponge-like material, which is different from the perforated metal having a number of holes drilled by press working.
In the present invention, since the porous damping material is attached to the surface (inner circumference) of the fan shroud opposing to the end of the fan to which the strong swirl is generated by pasting, or the surface of the fan shroud opposing to the end of the fan itself is made of the porous damping material, the jet noise caused by the swirl can be damped by sound absorbing properties of the porous damping material.
Further, since the conventional perforated metal is not used, the cooling air does not bump into the hard step portion, thus being unlikely to generate impulsive sound.
Accordingly, both of the impulsive sound and the jet noise can be effectively damped and the noise between the end of the fan and the fan shroud can be securely decreased.
The noise reduction mechanism of fan device according to the present invention may preferably have a radiator provided to upstream or downstream of the fan, a radiator hood and an end plate, the radiator hood and the end plate air-tightly connecting the radiator and the fan shroud.
According to the above arrangement, since the airtight space surrounded by the radiator hood and the end plate works as a damping space of the energy (pressure wave) of the noise, damping properties can be improved. Further, since the radiator hood is provided, the cooling air can flow more smoothly, so that the radiator can exchange the heat more efficiently.
In the above noise reduction mechanism of fan device, another porous damping material may preferably be attached to inner circumference of the radiator hood and/or inner circumference of the end plate.
Accordingly, since the porous damping material is attached to the inner circumference of the radiator hood and the end plate, the noise can be further decreased.
In the noise reduction mechanism of fan device according to the present invention, a number of holes may preferably be formed to the fan shroud with the porous damping material being attached.
Accordingly, low-frequency noise can be effectively decreased by forming the number of holes to the fan shroud.
In the noise reduction mechanism of fan device according to the present invention, the fan shroud and/or the porous damping material may preferably have bell-mouth shape.
According to the above arrangement, since the fan shroud and/or the porous damping material have bell-mouth shape, the cooling air can flow smoothly between the end of the fan and the fan shroud or the porous damping material, so that the generated jet noise can be reduced to further decrease the noise.
In the above, the porous damping material may have a cover portion for covering a surface thereof opposing to the end of the fan.
Accordingly, since the surface of the porous damping material is covered with the cover portion, absorption of water can be more securely prevented as compared to chemical water-repellant treatment on the surface of the porous damping material. Further, since the dust snapped by the fan does not-bump into the porous portion of the porous damping material, the porous damping material can be prevented from being degraded and damaged, so that weather resistance and durability can be improved.
Furthermore, since firmness of the porous damping material can be improved by the cover portion and the porous damping material is less likely to be flexed, the porous damping material is more easily attached to the fan shroud by, for instance, pasting, thus facilitating manufacture of the fan shroud.
In the noise reduction mechanism of fan device according to the present invention, the fan shroud may preferably have a protector for protecting at least one of upstream end and downstream end of the porous damping material in an air flow direction.
When the porous damping material is attached to the fan shroud, the upstream and downstream end of the porous damping material can be easily peeled off from the fan shroud by collision with the dust snapped by the fan. However, since the protector can prevent the collision of the dust, the porous damping material can be effectively prevented from being peeled off.
In the above, the fan shroud may preferably have an engage member for partially engaging the porous damping material.
Accordingly, since the engage member can maintain the attachment of the porous damping material, the porous damping material can be prevented from being peeled off from the fan shroud, thus improving reliability.
The fan shroud may have openings respectively provided on upstream and downstream side in the air flow direction and curved in bell-mouth shape, and a parallel portion provided between the openings, the parallel portion being parallel to the axis line direction of rotation axis of the fan, and the porous damping material may be attached to the parallel portion of the fan shroud.
Accordingly, since the parallel portion of the fan shroud forms the cylindrical portion having the same inner diameter, the porous damping material can be attached to the cylindrical portion. Therefore, it is not necessary that the porous damping material is pressed to the curved portion for attachment, thus facilitating attachment work.
In the above, the porous damping material may preferably formed in a smooth shroud extending over a part of the bell-mouth curved portion provided to upstream and downstream side in the air flow direction.
According to the above arrangement, since a part of the opening having the bell-mouth shape (i.e. a part of the bell-mouth configuration) is formed by the porous damping material, even when the portion made of the fan shroud itself is shortened by the length of the portion made of the porous damping material, the entire bell-mouth configuration can be maintained while keeping width dimension (width in a direction parallel to the axis line) of the porous damping material. Accordingly, the size of the fan shroud can be reduced by the length of the shortened opening by the fan shroud while securely maintaining the noise absorbing properties.
A noise reduction mechanism of fan device according to another aspect of the present invention includes: a fan shroud spaced apart from a rotation locus of an end of a rotary fan by a predetermined gap; a radiator provided on upstream or downstream of the fan; a radiator hood and an end plate for air-tightly connecting the radiator and the fan shroud; and a damping chamber constituted of semi-closed space surrounded by the radiator hood, the end plate and the fan shroud, the damping chamber being in communication with an inside of the radiator hood through a plurality of resonance pipe provided along circumferential direction of the damping chamber.
According to the above arrangement, the porous damping material attached to the fan shroud can decrease the noise composed of jet noise and impulsive sound and the noise can be further reduced by forming the semi-closed damping chamber.
In addition, since the damping chamber and the inside of the radiator hood are intercommunicated by the resonance pipe, a resonance frequency at the resonance pipe can be defined by appropriately setting diameter and length of the resonance pipe, volume of the damping chamber etc., so that noise having the same specific frequency as the resonance frequency is resonated in the resonance pipe, thus efficiently damping the noise energy.
Incidentally, in the above-described present invention, the porous damping material is attached to an inner circumference of the fan shroud (i.e. a portion confronting the rotation locus of the end of the fan) for effectively damp the jet noise caused between the fan shroud and the fan, thus securely reducing noise.
The porous damping material is, for instance, formed in a desired shape such as square cross section and size by cutting a large foamed urethane resin by a hot wire or a cutting machine having thin blade. The porous damping material having material flexibility is attached to the fan shroud of various shapes considering fan performance such as bell-mouth shape.
However, a lot of trouble is required for cutting the porous damping material into a desired shape by the above-described cutting machine.
Further, it is not economical to form the fan shroud into a shape considering the fan performance such as the bell-mouth shape. This is because, for instance, when the fan shroud is made of metal, great die cost is necessary on account of large size press die and, when the fan shroud is made of resin, the size of the molding die is enlarged and cost thereof is significant.
Another object of the present invention is to provide a noise reduction mechanism of fan device capable of being easily and economically manufactured.
In order to attain the above object, the noise reduction mechanism of fan device of the present invention employs the porous damping material made of die molding.
Specifically, a noise reduction mechanism of fan device according to the present invention has: a rotary fan; a fan shroud spaced apart from a rotation locus of an end of the rotary fan by a predetermined gap; a shroud support for supporting the fan shroud; and a porous damping material opposing to the end of the fan, the porous damping material being attached to at least a part of the fan shroud or forming a part of the fan shroud, the porous damping material being a die-molding product.
According to the above arrangement, since the porous damping material is a die-molding product, desired final shape of porous damping material can be easily obtained. Further, since the porous damping material can be easily molded in any shape considering fan performance such as bell-mouth shape, the fan shroud may be configured in a simple shape considering convenience in manufacture, so that conventionally required large press die or molding die is no longer necessary.
In the noise reduction mechanism of fan device according to the present invention, the porous damping material may preferably be formed linearly in a longitudinal direction thereof and may preferably be curved along the circumference of the fan shroud.
According to the above arrangement, the porous damping material may be molded in a linear elongated shape and cut into any desired length, so that the porous damping material can be easily applied to fan shrouds having different diameter.
In the noise reduction mechanism of fan device according to the present invention, the porous damping material may preferably be curved in a longitudinal direction thereof and be provided along the circumference of the fan shroud.
According to the above arrangement, the porous damping material may be molded in a curved shape in accordance with the diameter of the fan shroud, so that the porous damping material can be easily attached.
In the noise reduction mechanism of fan device according to the present invention, the porous damping material may preferably be constituted of a plurality of porous member provided along the circumference of the fan shroud.
According to the above arrangement, since the porous damping material is composed of the plurality of short porous member, the size of the die required for molding can be reduced, thus decreasing die cost. Further, since the porous member is short, transportation and storage thereof can be facilitated.
In the noise reduction mechanism of fan device according to the present invention, a configuration of the porous damping material confronting the end of the fan may preferably be a bell-mouth shape on both upstream side and downstream side of the fan shroud.
According to the above arrangement, the frequency of the fan can be lowered corresponding to increase in wind flow, thus further reducing noise.
In the noise reduction mechanism of fan device according to the present invention, the porous damping material may preferably be held on the fan shroud and/or the support by a belt-shaped dropout prevention means.
According to the above arrangement, the porous damping material is securely held by the dropout prevention means and, since the dropout prevention means is belt-shaped, the dropout prevention means may be wound around the porous damping material or the fan shroud, thus facilitating attachment work.
In the noise reduction mechanism of fan device according to the present invention, the porous damping material may preferably be held on the fan shroud and/or the support by a net-shaped dropout prevention means.
According to the above arrangement, the porous damping material can be also securely held by the dropout prevention means. Further, since the dropout prevention means is net-shaped, the entire porous damping material can be securely held, thus greatly improving dropout prevention effect.
On the other hand, since the porous damping material directly confronts the fan, the porous damping material can be deteriorated or damaged by colliding with dust or rainwater snapped by the fan, thus deteriorating weather-resistance and durability of the porous damping material.
Accordingly, the resin sheet or the cloth sheet made of various material is attached on the surface of the porous damping material by adhesion or thermal bonding to prevent the surface of the porous damping material from foreign body, thus improving weather-resistance and durability.
However, attachment work of the resin sheet or the cloth sheet onto the surface of the porous damping material by adhesion or thermal bonding is not easy and requires a lot of work, thus deteriorating productivity.
Further object of the present invention is to improve weather-resistance and durability of porous damping material used for the noise reduction mechanism of fan device.
In order to attain the above object, the present invention employs molding method of the porous damping material by die-molding.
Specifically, according to the present invention, a molding method of a porous damping material used for a noise damping mechanism of a fan device having: a rotary fan; a fan shroud spaced apart from a rotation locus of an end of the rotary fan by a predetermined gap; a shroud support for supporting the fan shroud; and a porous damping material opposing to the end of the fan, the porous damping material being attached to at least a part of the fan shroud or forming a part of the fan shroud, the method is characterized in having the steps of: disposing a foam material having larger volume than a cavity of a die while being elastically deformed; and heating the die to mold the foam material into the porous damping material.
The xe2x80x9ccavityxe2x80x9d referred herein is a portion having a volume of a final configuration of the porous damping material.
According to the above arrangement, since the foam material is disposed in the cavity while being compressed, the contact area against the cavity surface is enlarged on the surface of the foam material on account of dense foam. When the die is heated under the above condition, the heat is efficiently transmitted to the dense portion, so that the surface of the foam material is securely melted to securely mold the final configuration of the porous damping material. At this time, thin rigid layer is easily formed on the surface of the foamed material, which efficiently functions as a protection layer. Accordingly, the porous damping material can be effectively protected from the dust and rainwater snapped by the fan, thus improving weather-resistance and durability.
In the molding method of the porous damping material according to the present invention, the porous damping material may preferably be constituted of a plurality of porous member provided along the circumference of the fan shroud, the porous damping material being molded by the foam material using the die.
As mentioned above, according to the above arrangement, since the size of the die required for molding can be reduced, thus reducing die cost and facilitating transportation and storage of the porous member.